1. Field of the Invention
The present invention relates to a high temperature resistant seal structure of an axial directional slide shaft of a valve, etc., handling a high temperature fluid in a side thruster of an aerospace craft, etc. The present invention also relates to a valve comprising this seal structure as well as relates to a side thruster of an aerospace craft comprising this valve.
2. Description of the Related Art
FIG. 2 is a longitudinal cross sectional view of a prior art side thruster valve used in an aerospace craft, etc. and description will be made based thereon.
As shown in FIG. 2, a thruster valve 01 comprises a valve casing 02. The valve casing 02 comprises a supply port 03 through which working medium a is supplied and a nozzle 04 from which the working medium a is discharged. Within the valve casing 02, the supply port 03 and a nozzle throat portion 05 of the nozzle 04 communicate with each other.
Also, within the valve casing 02, a valve plug 06 opening and closing the nozzle throat portion 05 is arranged being connected to one end of a drive rod 07. The drive rod 07 slidably passes through a drive rod through hole 09 of the valve casing 02 and the other end of the drive rod 07 projecting outside of the valve casing 02 is connected to an actuator 08 of a linear actuator, rotary actuator or the like so that the drive rod 07 is driven along the axial direction thereof as shown by a bidirectional arrow X. The actuator 08 is fixed to a fixing member (not shown).
The working medium a supplied through the supply port 03 flows through a space formed between the nozzle throat portion 05 and the valve plug 06 and is jetted from the nozzle 04 so that a thrust of the side thruster is generated. At this time, the actuator 08 drives the valve plug 06 so as to open and close the nozzle throat portion 05 and to change the area of the flow path of the working medium a. Thereby, the thrust can be changed continuously or step-wise.
In the drive rod through hole 09 of the valve casing 02, an elastomer seal 010 is provided so as to form a seal structure preventing the working medium a from leaking through between the valve casing 02 and the drive rod 07. It is to be noted that the term “elastometer” means a high molecular substance having a rubber elasticity.
Conventionally, in the slidable portion between the valve casing 02 and the drive rod 07 of the thruster valve 01 as mentioned above, such a metal seal as usually used for sealing between stationary faces cannot be used, as the sealing is not sufficiently achieved because of the sliding motion of the sealing face. Hence, the elastomer seal 010 of an O-ring or the like is used.
For this reason, if a high temperature fluid, such as combustion gas, is used as the working medium a, the elastomer seal 010 often melts because of the heat transmitted from the drive rod 07 so that the combustion gas leaks to form a leak gas b. Thus, the actuator 08 is exposed to the high temperature environment by the leak gas b and there is caused a risk of operation disorder of the actuator 08.
Also, if a structure to protect the elastomer seal 010 and the actuator 08 is to be employed, the valve casing 02 has to be made larger by that extent and there is a problem that this leads to a larger size and mass increase of the side thruster device.
Also, as the side thruster device uses the valve casing 02 made of a metal, the slide resistance between the valve casing 02 and the drive rod 07 becomes large under the high temperature in the drive rod through hole 09. Thus, the drive force of the thruster valve 01 is inevitably made larger and there is caused a problem that this again leads to a larger size of the actuator 08.